The invention relates to an electronic thermometer. The conventional mercury thermometer gives in general a satisfying precision but presents various disadvantages. In particular, a mercury thermometer is sometimes difficult to read and hence presents some risk of error. There have been prior efforts to replace the mercury thermometer by electrical or electronic temperature measuring devices.
For example, the thermocouple is known; in use, one of the two weldings of the thermocouple is placed in contact with the area of which the temperature is to be measured, and the other welding is put in a medium kept at a precise, known reference temperature. For example, melting ice under normal pressure, provides the reference temperature of 0.degree. C. The measurement of the voltage between the two weldings indicates the difference of temperature between the weldings, which allows calculation of the temperature to be measured by comparison with the reference temperature. However, the necessity of providing such a reference temperature is an inconvenience.
Another known method uses the fact that the usual resistive elements have a resistance varying with the temperature. It is also known that semi-conductors such as diodes and transistors, present characteristics which depend on the temperature. Further, resistive elements are available on the market which have a resistance which varies substantially over a specified range with the temperature, according to a characteristic, either positive or negative, but usually the elements with negative characteristics are used. A method for measuring the temperature utilizing such elements usually comprises the measuring of the current traversing such an element under a given voltage to derive its resistance or impedance and hence its temperature. There are alternative methods, but all present the same inconvenience of requiring a voltage or current reference sourch which is very stable and very precise.